What are the products of the thermal decomposition of calcium carbonate?

• A. Calcium Oxide and Carbon Dioxide
• B. Calcium Carbonate and Water
• C. Calcium Hydroxide and Carbon Monoxide
• D. Calcium Nitrate and Oxygen

Answer: (A)

Thermal decomposition is when a compound breaks apart into simpler substances as heat is applied. Metal carbonates, like calcium carbonate, lose carbon dioxide when heated, leaving behind the metal oxide. So calcium carbonate decomposes to calcium oxide and carbon dioxide: CaCO3 → CaO + CO2. The CO2 escapes as gas, which is why you often see effervescence when heating it. The other options don’t match what calcium carbonate does on heating: water isn’t produced from simply heating CaCO3; calcium hydroxide would form only if you first produced CaO and then added water; carbon monoxide isn’t the usual product here; and calcium nitrate and oxygen come from decomposing nitrates, not carbonates.